When computer or video generated information is displayed on a color monitor on which the display is transient, it is desirable in many cases to maintain permanent records of the information displayed. In the case where industrial processes are monitored by color display, a permanent record would be valuable for later examination to document or study a particular condition or event. Present systems employ various methods of photographing the display tube face to yield color hardcopy. These methods may be as simple as photographing the tube face directly, or through sequenced color filters, or photographing a special high resolution black and white display tube sequentially through appropriate color filters to reconstruct the color image. These methods all suffer from the limitations imposed by the displayed device. These limitations relate to such items as image resolution and color quality, the problems associated with holding the particular image on the display tube while the photograph is being made, and how to obtain the picture without interfering with the operators' view of the display.
Another system of producing a color hardcopy from an original is disclosed in U.S. Pat. No. 3,842,195 issued Oct. 15, 1974, to Tsunehiko Takahashi. This system employs a laser beam which is modulated by a color signal from an original and the beam is radiated onto a photosensitive material which yields different colors according to the intensity of light radiated thereon. A special photosensitive material is used to record the color which will yield different colors in response to the intensity of the laser beam. However, since the recording medium is divided into two or three materials which are responsive to different intensities, the reproduction would not be full color with a tone scale. Another method for producing color hardcopy is illustrated in U.S. Pat. No. 3,679,818 issued July 25, 1977 to Jeofry Stuart Courtney-Pratt. This system utilizes a film with a repeating color dot pattern on one side and opaque coating on the other side. Laser light having the same frequency as the dot color is directed through those dots constituting the desired image, and the metal coating behind each such dot is thereby evaporated, leaving the dot color uneffected. Preferrably, a laser with three independent beams each of which corresponds in frequency to one of three basic colors is utilized and the contribution of each color component is adjusted by using only the corresponding frequency scanning beam operated at levels sufficiently intense to evaporate the metal coating. This patent also suggests a single laser to remove the region of the opaque layer behind the dots to constitute the desired image. This system does not have any tone scale since upon the melting of the layer, the full color of the dot is produced. Other patents of interest in connection with this field are as follows:
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